Three-phase bimetal overload relay

ABSTRACT

AN OVERLOAD RELAY HAVING THREE IDENTICAL OPERATING BIMETAL ELEMENTS, A SNAP SWITCH, AND A LEVER ARRANGEMENT FOR TRANSMITTING THE MOVEMENTS OF THE OPERATING BIMETAL ELEMENTS TO THE PUSH BUTTON OF THE SNAP SWITCH WHEN THE OPERATING BIMETALS ARE HEATED. AN AMBIENT-COMPENSATING BIMETAL ELEMENT THAT IS IDENTICAL TO THE OPERATING BIMETAL ELEMENTS HAS AN OPERATIVE CONNECTION WITH THE LEVER ARRANGEMENT FOR COMPENSATING THE EFFECT OF MOVEMENT OF THE OPERATING BIMETAL ELEMENTS FOR VARIATIONS IN AMBIENT TEMPERATURE. THE RELAY ALSO INCLUDES A MEANS FOR CAUSING THE SNAP SWITCH TO BE ACTUATED WHEN LESS THAN ALL OF THE OPERATING BIMETAL ELEMENTS ARE HEATED TO A TEMPERATURE LOWER THAN THE TEMPERATURE REQUIRED TO ACTUATE THE SNAP SWITCH WHEN ALL OF THE OPERATING BIMETALS ARE HEATED AND A MEANS TO VARY THE TIME REQUIRED TO ACTUATE THE SNAP SWITCH IN ACCORDANCE WITH THE RATE AT WHICH THE BIMETALS ARE HEATED.

Jan. 12, 1971 H. E. WHITING ETAL Re. 27,024

THREE-PHASE BIME'IAL OVERLOAD RELAY Original Filed Oct. 18, 1966 3Sheets-Sheet l I NVENTOR. HAROLD E. WHITING MLTER C. HARCH DQVID B.McFADDEN BY aye/(Ja i? Jan. 12, 1971 H. E. WHITING HAL THREE-PHASEBIMETAL OVERLOAD RELAY Original Filed Oct. 18, 1966 5 Sheets-Sheet 2FIG. 4

PM]! iH me] I use Imol 7 so I N VENT OR. HAROLD E. WHITING WALTER Q.HARCH DAVID B. McFADDEN Jan. 12, 1971 Original Filed Oct. 1.8, 1966 -ISOJaw ,aeq gxso H. E. WHITING ETA!- THREE-PHASE BIME'IAL OVERLOAD RELAYFIG. 5

3 Sheets-Sheet 3 FIG. 6

INVENTOR. HAROLD E. WHITING WALTER C. KARCH DAVID B. McFADDEN UnitedStates Patent Olfice Re. 27,024 Reissued Jan. 12, 1971 27,024THREE-PHASE BIMETAL OVERLOAD RELAY Harold E. Whiting, Milwaukee, andWalter C. Karch, Grafton, Wis., and David B. McFadden, Freeport, Ill.,assignors to Square D Company, Park Ridge, Ill., a corporation ofMichigan Original No. 3,422,317, dated Jan. 14, 1969, Ser. No. 587,471,Oct. 18, 1966. Application for reissue Oct. 8, 1969, Ser. No. 882,759

Int. Cl. H02h 3/00, 3/28, 71/16 US. Cl. 317-46 12 Claims Matter enclosedin heavy brackets appears in the original patent but forms no part ofthis reissue specification; matter printed in italics indicates theadditions made by reissue.

ABSTRACT OF THE DISCLOSURE An overload relay having three identicaloperating bimetal elements, a snap switch, and a lever arrangement fortransmitting the movements of the operating bimetal elements to the pushbutton of the snap switch when the operating bimetals are heated. Anambient-compensating bimetal element that is identical to the operatingbimeta'l elements has art operative connection with the leverarrangement for compensating the efiect of movement of the operatingbimetal elements for variations in ambient temperature. The relay alsoincludes a means for causing the snap switch to be actuated when lessthan all of the operating bimetal elements are heated to a temperaturelower than the temperature required to actuate the snap switch when allof the operating bimetals are heated and a means to vary the timerequired to actuate the snap switch in accordance with the rate at whichthe bimetals are heated.

This invention relates to thermally operated protective devices and moreparticularly to devices of the type used to open a circuit upon acurrent overload in any number of a plurality of circuits as may be usedto supply a multiphase electric motor.

Thermally operated devices, known as overload relays, are used toprotect electric apparatus, such as electric motors, against continuedoperation when the line current drawn is excessively high as maybecaused by overloading the machine driven by the motor, excessively lowline voltage, or single phase operation of a polyphase motor. As theoverload relays and the apparatus protected thereby may be subjected todifferent environments, the switch according to the present invention isprovided with means for compensating for the effect of ambienttemperature whereby the switch will respond to the same overloadconditions, regardless of variations in the temperature of thesurrounding atmosphere. In addition, the switch according to the presentinvention is provided with a means to cause the switch to performdifferently during conditions of high current overloads than duringmodest overload conditions with the means being arranged to cause theoperation of the switch to be accelerated during high current overloadconditions.

The switch according to the present invention also provides an advantageas the switch will operate when less than all of the operating bimetalelements are heated to a temperature that is lower than the temperaturerise required to actuate the switch when all of the operating bimetalelements are heated. Thus the switch according to the present inventionwill operate in response to lower currents when a polyphase motor isoperating as a single phase motor under conditions that would damage themotor than when all phases of the motor are energized.

Because of variations in materials and manufacturing tolerances, bimetalelements of different designs may not react alike to differenttemperature changes. Thus in manufacturing a switch wherein the shapeand/or characteristics of the ambient compensating bimetal element isrequired to be different than the operating bimetal elements,difficulties will arise in matching the characteristics of the twodifferent designs of bimetal elements to obtain a switch that may bereadily calibrated and function properly throughout its entire currentand temperature range. In the switch according to the present invention,as the operating bimetal elements and the ambient compensating bimetalelement are identical, the selection of the bimctal elements andcalibration of the switch during manufacture is simplified.

It is an object of the present invention to compensate the operation ofa bimetallic type overload relay for virations in ambient temperaturewith a bimetal element that is identical to the current monitoringbimetal elements of the overload relay.

An additional object is to provide an overload relay with a plurality ofheat responsive operating bimetal elements, a snap switch, a leverarrangement for transmitting movements of the bimetal elements to anoperator of the snap switch when the bimetal elements are heated and ameans for causing the snap switch to be actuated when less than all ofthe bimetal elements are heated to a temperature that is lower than thetemperature required to actuate the snap switch when all of the bimetalelements are heated.-

A further object is to provide an overload relay with a plurality ofheat responsive bimetal operating elements, a snap switch, a leverarrangement for transmitting movements of the bimetal elements to anoperator of the snap switch when the bimetals are heated and a means forvarying the time required to actuate the snap switch with variations inthe rate at which the bimetals are heated.

Another object is to provide an overload relay with a plurality ofidentical heat responsive operating bimetal elements, a snap switch, alever arrangement for transmitting movements of the operating bimetalelements to the operator of the snap switch when the operating bimetalsare heated, and means including an additional bimetal element that isidentical to the operating bimetal elements and has an operatingconnection with the transmitting lever arrangement for compensating themovement of the operating bimetal elements for variations in ambienttemperature and for causing the snap switch to be actuated when lessthan all of the bimetal elements are heated to a temperature that islower than the temperature required to actuate the snap switch when allof the bimetals are heated.

And another object is to provide an overload relay with a plurality ofidentical heat responsive operating bimetal elements, a snap switch, alever arrangement for transmitting movements of the operating bimetalelements to the operator of the snap switch when the operating bimetalsare heated, means including an additional bimetal element that isidentical to the operating bimetal elements and has an operatingconnection with the transmitting lever arrangement for compensating theeffect of movement of the operating bimetal elements for variations inambient temperature, a means for causing the snap switch to be actuatedwhen less than all of the bimetal elements are heated to a temperaturethat is lower than the temperature required to actuate the snap switchwhen all of the bimetals are heated, and a means for varying the timerequired to actuate the snap switch with variations in the rate at whichthe bimetals are heated.

Further objects and features of the invention will be readily apparentto those skilled in the art from the specification and appended drawingsillustrating certain preferred embodiments in which:

FIG. 1 is a schematic perspective view of an overload relay mechanismaccording to the present invention.

FIG. 2 is a diagrammatic diagram of certain elements of the overloadrelay mechanism in FIG. 1.

FIG. 3 is a top plan view of an overload relay mechanism incorporatingthe elements illustrated in FIGS. 1 and 2.

FIG. 4 is a front elevational view of the overload relay mechanism shownin FIG. 3.

FIG. 5 is a top plan view of the overload relay mechanism with a topportion of a housing for the overload relay removed and taken along line5-5 in FIG. 4.

FIG. 6 is a view partly in cross-section taken along line 6-6 in FIG. 3.

FIG. 7 is a cross sectional view taken generally along line 7--7 in FIG.3.

In FIGS. 1 and 2 a functional model of a thermally operated protectiveswitch or device 10 according to the present invention is illustrated.The switch 10 has a hous ing 12, of molded insulating material, whereina pair of spaced levers 14 and 16 rotate about a pair of spaced andparallel pivot axes. As shown, the lever 14 is provided with a pivot 18and the lever 16 with a pivot 20. The pivots 18 and 20 are carried by amember 21 secured to a bottom wall of the housing 12. An additionalsimilar member, not shown, carrying similar pivots, is provided at theother end of the housing 12 to permit relative independent movementbetween a free end portion 22 on the lever 14 and a free end portion 24on the lever 16.

Positioned between the levers 14 and 16 are four identical U-shapedbimetal elements 26, 28, and 32. Each of the bimetal elements 26-32 isformed of bimetal strip material to have a pair of spaced armsdesignated by suffices a and b that spread in the direction ofindicating arrows 26c, 28c, 30c and 32c when the bimetal elements areheated. The bimetal elements 26-32 are arranged to have the bimetals 26,28 and 30 act as operating bimetal elements each responding to theheating effects of currents through separate circuits and the bimetalelement 32 provides ambient compensation for the switch 10. The bimetals26, 28 and 30 are respectively coupled with heating elements 34, 36 and38, as shown in FIG. 2.

In FIG. 1, for purposes of clarity, only a single heatin element 34 isshown as coupled with the bimetal element 26. When the switch 10 is usedwith a three-phase motor, not shown, the heating elements 34, 36 and 38are connected to be heated by the current flow in the individual motorwindings. The heating elements 34, 36 and 38 as shown are U-shaped andare positioned in heat radiating relation between the spaced arms of theU- shaped bimetal elements to heat the bimetal elements 26, 28' and 30in response to current flow through the motor windings. The ends of arms26a, 28a and 30a of the bimetals 26, 28 and 30 are secured to theportion 22 of the lever 14 as by rivets 40. The ends of arms 26b, 28band 30b of the [levers] bimetals 26, 28 and 30 are not fixed and restagainst the portion 24 of the lever 16. The lever 16 has a portion 42engaging an operator 44 of a snap switch 46. The snap switch 46preferably is of the type requiring minimal movement of the operator 44before moving its contacts with a snap action from a circuit closingposition to a circuit opening position when a predetermined force isapplied to the operator 44.

The ends 26b, 28b and 30b are positioned between the portion 24 andfixed stops 48 formed as part of the housing 12. As shown in FIG. I, thestops 48 are located to limit the movement of ends 26b, 28b and 30btoward the lever 14.

The ambient temperature compensating bimetal element 32 has arms 32a and32b which spread in response to an ambient temperature increase. The arm32a is secured to the lever 14 by a rivet S0. The arm 32b is adjustablypositionable relative to the housing 12 by an adjustment means 52. Theadjustment means 52 inc udes a rotatable member 56 having a threadedportion 58, an adjustment knob 60, a portion 62 extending through anopening in the arm 32b and a stop 64 on the end of portion 62. The stop64 is positioned to engage an inner surface of the arm 32b and limitmovement of the arm 32b toward the arm 32a. The opening in the arm 32receives the portion 62 with clearance permitting the arm 32b to moveout of engagement with the stop 64. The knob 60 is used to rotate themember 56 and because of a threaded connection between the housing 12and the threaded portion 58, the relative positions of the stop [62] 64and the arm 32b may be adjustably varied.

The switch 10 also includes an additional bimetal elemeat 66, known as atripping accelerator bimetal. The bimetal element 66 may have adifferent shape and load characteristics than the bimetal elements 26,28, 30 and 32 and has an arm portion 66a secured to the housing 12 andan arm portion 66b engageable with the lever 14. The bimetal element 66has the same deflection characteristics as the bimetal elements 26, 28,30 and 32 and is constructed to have the ends of the arms 66a and 66bmove toward each other when the bimetal element 66 is heated. Thebimetal element 66 is positioned in the housing 12 to be heated by theheaters 34, 36 and 38 at a slower rate than the bimetal elements 26, 28and 30.

Referring to FIG. 2, the operation of the switch 10 Will now bedescribed. During normal ambient temperature and nonopebatingconditions, the heating elements 34, 36 and 38 will not be subjected tocurrent and the arms of the bimetal elements 26, 28 and 30 as well asthe bimetal element 66 will be relaxed. Thus the levers 14 and 16 willnot be subjected to any force and will in effect float in the housing 12and the lever 16 will be free to engage either the actuator 44 or thearm portions 26b, 28b and 30b Without exerting a force on either the armportions or the actuator. Similarly, the lever 14 will be disengagedfrom the arm 66b and position the arm 32b a predetermined distance fromthe stop 64.

When all of the heaters 34, 36 and 38 are heated by normal motorcurrent, the arms 26a26b, 28a28ib and 30a-30b will spread, causing amovement of the arms 26a, 28a, 30a to the left and a movement of thearms 26b, 28b and 30b to the right. The movement to the right of thearms 26b, 28b and 30b causes the lever 16 to move to the right andimpress a force against the actuator 44. The force on the actuator 44 isresisted by the mechanism of the snap switch 46. As previously stated,the snap switch 46 is selected to require a predetermined applied forceon actuator 44 before the contacts will move with a snap action from acircuit closing to a circuit opening position and the snap action of thecontacts will occur upon a minimal distance of travel of the actuator44.

As the lever 16 is prevented from movement to the right by the opposingforce supplied by the actuator 44, the arm portions 26a, 28a and 3021will move lever 14 and the bimetal element 32 to the left to a positionwherein the arm 32b engages the stop 64. The foregoing movement of thelever 14 and the bimetal element 32 will be unopposed by the bimetalelement 32 because of the lost motion connection provided by thedistance the arm 32b is required to move on the portion 62 beforeengaging the stop 64. Further movement of the lever 14 to the left afterengagement of the arm 32b with the stop 64 is resisted by the bimetalelement 32 which acts as a resilient means having identical springcharacteristics as the bimetal elements 26, 28 and 30. The movement tothe left of the lever 14 continues until the force exerted by thebimetals 26, 28 and 30, that is resisted by the bimetal 32, stabilizesat a value less than the force required to move the operator 44 andactuate the snap switch 46.

When a current higher than normal occurs in each of the heaters 34, 36and 38, the force exerted by the bimetals 26, 28 and 30, as resisted bythe bimetal 32,

progressively increases to the value required to move the operator 44and actuate the switch 46.

In the event of failure of one of the phases of the mot-or protected bythe switch 10, two of the heating elements will be heated and theremaining heating element will not be heated. Assuming a conditionwherein the circuit connected to the heating element 38 is open and notcarrying current and the circuits connected to the heating elements 34and 36 are subjected to an excess current, the switch will operate asfollows. The heating effect of the abnormal excess current through theheating elements 34 and 36 causes movement of the arms 26a and 28a tothe left and movement of the arms 26b and 28b to the right. The movementto the right of the arms [26a] 26b and 28b causes the lever 16 to moveto the right and impress a force against the actuator 44. As themovement of the lever 16 is opposed by the actuator 44, the arm portions26a and 28a will urge the lever 14 and the bimetal element 32 toward theleft. The motion of the lever 14 to the left is instantly opposed by thebimetal element 30 as the arm portion 30b engages the stop 48. After thelever 14 has moved a predetermined distance to the left to a positionwherein the arm 32b engages the stop 64, further movement of the lever14 to the left will be resisted by both bimetal elements 30 and 32 eachacting as a resilient means having identical spring characteristics asthe operating bimetals 26 and 28. The movement to the left of the lever14 will continue until the force exerted by the bimetal elements 26 and28, as resisted by the bimetal elements 30 and 32, equals the forcedrequired to move the operator 44 to actuate the snap switch 46.

While useful in other types of motor circuits, the switch according tothe present invention is particularly suited for use in a circuitwherein a Ydelta transformer provides a supply for a three-phase motor.In event of failure in one of the phases of the primary side of thetransformer, two of the phases of the motor will be excited with aslightly increased current while the remaining phase will be excitedwith current in excess of twice the normal value. Thus under conditionswherein a threephase motor supplied by Y-delta transformer is operatingunder a load significantly less than its rated load, and a failureoccurs in one of the phases of the primary side of the transformer, twoof the phases of the motor will be supplied with less than the normalcurrents required to trip the switch 10 while the third phase will besupplied with current in excess of the normal currents. In the event theswitch 10 has its heating elements 34, 36 and 38 connected in circuitshaving an excess current in one of the circuits and less than normalcurrent in the two remaining circuits, one of the heating elements willbe heated excessively and the two remaining heating elements will beheated less than normal. Assuming a condition wherein the circuitsconnected to the heating elements 36 and 38 are carrying less thannormal currents and the circuit connected to the heating element 34 issubjected to an excess current, the switch 10 will operate as follows:the heating effect of the excess current through the heating element 34will cause movement of the arm 26a to the left and movement of the arm26b to the right. The movement to the right of the arm [26c] 26b causesthe lever 16 to move to the right and impress a force against theactuator 44. As the movement of the lever 16 is opposed by the actuator44, the arm portion 26a will urge the lever 14 and the bimetal element32 toward the left. This motion of the lever 14 to the left is opposedby the bimetal elements 28 and 30 as the arm portions 28b and 30b engagethe stop 48. After the lever 14 has moved a predetermined distance tothe left to a position wherein the arm 32b engages the stop 64, furthermovement of the lever 14 to the left will be resisted by bimetalelements 28, 30 and 32 each acting as a resilient means having identicalspring characteristics as the operating bimetal 26. The movement to theleft of the lever 14 6 will continue until the force exerted by thebimetal element 26, as resisted by the bimetal elements 28, 30 and 32,equals the force required to move the operator 44 and actuate the snapswitch 46.

The switch 10 has its levers and bimetal elements arranged to actuatethe snap switch 46 when any number less than all of operating bimetalelements 26, 28 and 30 are heated to a temperature that is less thanwhen all of the operating bimetal elements 26, 28 and 30 are heated.This can be mathematically demonstrated in the following exampleswherein:

F-pounds of force required to trip the snap switch AT,,temperaturechange required to heat operating bimetal elements to trip switch dtotaldistance bimetal arms 26a, 28a and 30a move to provide force to tripsnap switch r-distance ambient compensating bimetal arm 32a moves whenoperating bimetals are heated idistance bimetal arms 26a, 28a and 30amove to take up lost motion connection between the arm 32a and stop 64aforce constant in lbs/degrees F of the bimetals 26,

28, 30 and 32 c-motion constant in inches/degrees F of the bimetals 26,28, 30 and 32 K-bimetal spring constant a/c=lbs./inch THREE OPERATINGBIMETAL ELEMENTS HEATED The three operating bimetal elements 26, 28, and30 each are equally heated and equally share the required force F. Thusto develop the required force F the bimetal elements 26, 28 and 30 mustbe heated F/3a. Further, the three operating bimetal elements 26, 28 and30 must be additionally heated to deflect the unheated bimetal 32 adistance sufiicient to provide the force F.

Therefore F i r -amt;

substituting for r F i F sz a s Solving 4F i r. 5

Bimetal element 32 supplies entire force F ..F=rK

Solving for r r= [F/K] Substituting a/c for K r: [Fe/a] TWO OPERATINGBIMETAL ELEMENTS HEATED (ASSUME BIMETAL ELEMENTS 26 AND 28 HEATED) Thetwo operating bimetal elements 26 and 28 each equally share the requiredforce F and to develop the required force F must be heated F/2a.Further, the two operating bimetal elements 26 and 28 must beadditionally heated to deflect the bimetal elements 30 and 32 asufficient distance to provide the force F F i r -afia z Substitutingfor r F i F i -n a n-a Bimetal elements 32 and 30 share force F.'.F=rK+(i+r)K Solving for r ONE OPERATING BIMETAL HEATED (ASSUMEBIMETAL ELEMENT 26 HEATED) Substituting for r Bimetal elements 32, 30and 28 share force F .'.F=rK+(i-|-r)K-l-(i+r)K Solving for rSubstituting for K In previous designs of bimetal overload switches thespeed with which the switch is actuated when excess current occurs is afunction of the degree of excess current and the rate of heat transferfrom the heating elements through which the excess current flows and thebimetal responsive elements. In the switch according to the presentinvention the speed is accelerated by the action of the bimetal 66 whichfunctions as follows.

When the heating elements are carrying normal currents, as previouslydescribed, a portion of the heat generated is transferred by convectionaround the actuating bimetals 26, 28 and 30 to the accelerating bimetal66. The accelerating bimetal 66 reacts by deforming with the ends of thearms 66a and 66b moving toward each other with the arm 66b retreatingfrom the lever 14 at at least the same rate as lever 14 is advanced bythe actuating bimetal elements 26, 28 and 30. Thus the bimetal 66 willnot influence the operation of the switch during normal operatingconditions.

If, however, the switch is in a cold, unoperative state and a suddenabnormal excess current, such as six times normal current, is caused toflow through the heater elements 34, 36 and 38 over an abnormal periodof time, bimetal elements 26, 28 and will be .fully exposed to heatingetfects of the current for the entire period of current flow and respondby deflecting while the convection heat will be delayed in reaching theaccelerator bimetal 66. Accordingly, the accelerator bimetal 66 will notmaterially deflect. Therefore lever 14, which under the normalconditions previously described was restrained only by bimetal 32, nowunder abnormal conditions as caused by a sudden flow of excess currentfor an abnormal period through the heating elements 34, 36 and 38, isadditionally restrained by bimetal 66. Thus a lower temperaturedifference and less time is required to cause sufficient force to bedeveloped by the bimetal elements 26, 28 and 30 on operator 44 toactuate switch 46. Also, if desired, the arm 66a may be adjustablyattached to housing 12 to provide an adjustable lost motion spacebetween arm 66a and lever 14. When this adjustment, not shown, isprovided, the effect of bimetal 66 under abnormal conditions of excesscurrent may be varied to permit the operating time response of theswitch It} to conditions of sudden abnormal excess current to beadjusted to compensate for diiferent types of loads that may be imposedon the motor.

In FIGS. 37 an operative embodiment of the switch incorporating thefeatures of the present invention as described in connection with theembodiment in FIGS. 1 and 2 is shown wherein the elements correspondingto similar elements in FIGS. 1 and 2 are similarly designated.

The housing 12 of the switch 10 in FIGS. 3-7 is formed of two moldedparts designated as a base 12a and a cover 12b. The base 12a is securedto a mounting plate 71 by means of the screws extending through themounting plate 71 and the bottom wall of the base 12a into the members21. The base 12a has an internal cavity. As shown in FIG. 5, the cavityis divided into two cavity portions 12c and 12b by a barrier 12d. Thebarrier 12d serves as a heat barrier and isolates the cavity 12c,wherein the ambient compensated bimetal 32 is received, from the cavity12b wherein the operating bimetals 26, 28 and 30 are received.Positioned within the cavity 12b is the lever 16. The lever 16 hasspaced projections 16a thereon extending with clearance through suitableopenings in the arms 26b. 28b and 30b of the operating bimetal elementspermitting the lever 16 to be moved by one or more of the arms 26b, 28band 30b independently of the remaining arms. The lever 16 additionallyhas a pair of spaced projections 16b thereon which act as heat barriersand are located to effectively divide the cavity 12b into threecompartments each having a bimetal 26, 28 and 30 positioned therein.Additionally, the portion 42 on the lever 16 engaging the actuator 44 ofthe snap switch 46 is adjustable.

The lever 14 extends across compartments 12b and 12c and includes threespaced projections 14a b and c. The projections 14a and 14b arepositioned adjacent the projections 16b and cooperate with theprojections 16b to provide a heat insulating barrier between thecompartments wherein the bimetal elements 26, 28 and 30 are located. Theprojection 14c is positioned adjacent the barrier 12d and cooperateswith the barrier 12d to provide a heat barrier between the ambientcompensated bimetal element 32 and the heating elements for operatingbimetal elements 26, 28 and 30. The arms 26a, 28a and 30a each aresecured to the lever 14 by the rivets 40. Similarly, the arm 32a of thebimetal 32 is secured to the lever 14 by the rivet 50. As shown in FIG.6, the adjustment means 52 for the bimetal 32 includes the knob 60, thethreaded portion 58, which is threadedly received in a nut 59 carried bythe housing part 12a, and the portion 62 carrying the stop 64. In theembodiment shown, the stop 64 is formed as a clip 64a that is receivedin a suitably formed groove in the portion 62.

Referring to FIGS. 5 and 7, the snap switch 46, which per se is not partof the present invention, includes a pair of spaced stationary contactsand 72 and a movable contact 74 carried on a resilient member 76 toalternately engage the contacts 70 and 72.

The resilient member 76 is formed to have a pair of parallel slotsextending between an end 78 carrying the movable contact 74 and an end80 secured to a support 82. The slots divide the member 76 to providethe member 76 with a pair of outer legs 84 extending between the ends 78and 80 and a central leg 86. The central leg 86 extends from the end 80to present a free end 88- spaced from the end 78. The resilient member76 also has portions of the outer legs 84 and the central leg adjacentthe end 80 formed as folded portions 90 to permit the length of the legs84 and the leg 86 to independently vary. interconnecting the free end 88and the end 78 is a C-shaped member 92. The member 92 constantly causesthe leg 86 to be subject to a compressive force while the legs 84 areunder tension. Thus the resilient member 76 and the member 92 act as atoggle mechanism alternately resiliently forcing the leg 86 either inone direction to a position wherein the contact 74 engages the contact70, or in an opposite direction to a second position wherein the contact74 engages the contact 72.

The support 82 is formed of a conducting metal part having a bodyportion 94 extending perpendicular to a pair of spaced feet 96 and 98.The feet 96 and 98 are secured to portions of the base 122. by screws100. The screw 100 securing the foot 96 electrically connects thesupport 82 to a terminal and wire clamping member 102 shown in FIG. 4.As shown in FIG. 7, a flexible strip 104 has the stationary contact 70secured at one end and its other end secured to a terminal and wireclamping member 106 shown in FIG. 4. The stationary contact 72 iscarried in spaced relation to the contact 70 on the opposite side of theresilient member 76 by a support 108. The support 108 also is connectedto a terminal and wire clamping member 110 shown in FIG. 4.

When the contact 74 engages the contact 70 the switch will be in acondition known as the tripped position, wherein a circuit between theterminals 102 and 110 is completed through the support 82, the resilientmember 76, the contacts 74 and 70 and the support 108. As shown in FIG.7, the components of the snap switch 46 are placed in the resetcondition by depressing a plunger 112 against the force of a returnspring 114 to a position wherein a projection 116 on a side wall of theplunger 112 engages a bearing surface 118 on the strip 104 and causesmovement of the contact 70 and the contact 74 toward the contact 72. Themovement of the contact 74 causes the member 76 and the C-shaped member92 to move to an overcenter position whereby the member 76 automaticallymoves with a toggle action to a reset position and resiliently maintainsthe engagement between the contact 74 and the contact 72. Further travelof the central leg 86 after the contacts 72 and 74 are engaged islimited by a stop 120 provided by the head of a screw having a threadedshank extending through an opening in the central leg 86 and adjustablythreaded into an opening in the body portion 94. The operator of thesnap switch 46 corresponding to the operator 44 in FIGS. 1 and 2 isprovided by the portion 42 having one end engageable with a portion ofthe central leg 86 located intermediate the stop 120 and the foldedportion 90. The portion 42 is adjustably threaded into an insert in thelever 16 whereby the point of operating engagement of the operator 44aand the central leg 86 may be adjusted when the lever 86 is moved towardthe reset condition.

The accelerating bimetal element 66, as shown in FIG. 7, is formed as anL-shaped member having a base portion 122 positioned in a groove in abottom outside surface of the base 12a between the base 12a and themounting plate 71 and an arm 124 spaced from the bimetals 26, 28 and 30extending between the lever 14 and the walls forming the cavity 12. Thearm 124 has a portion located to engage a projection 126 on the lever14. The material forming the bimetal element 66 is selected to have thearm 124 move away from the projection 126 when the bimetal 66 is heatedto function as previously described in connection with FIGS. 1 and 2.

The cover 12b is secured to a top wall of the base 12a by screws 128extending through suitable openings in the cover 12b into threadedengagement with threaded inserts 130 in the base 12a. The cover 12b hasthree spaced open ended compartments 132a, 132b and 132c extendingacross its top surface to be respectively vertically aligned with thebimetal elements 26, 28 and 30 and a portion 134 providing a top wallfor the cavity 12c. The compartments 132a, 132b and 132c aresubstantially identical and each have openings 136 therein verticallyaligned with the space between the arms a and b of the bimetal elements26, 28 and 30 and the ledges 138 and 140 extending on opposite sides ofthe openings 136. The ledges 138 and 140 are provided with a suitablemeans for securing conductor members 142 and 144 in the respectivecompartments on opposite sides of the openings 136. The conductormembers 142 and 144 have suitable threaded openings for receiving screws146. The screws 146 provide an attachment for connecting opposite endsof the heater elements 34, 36 and 38 between the conductor members 142and 144. Each heater element 34, 36 and 38 is U-shaped, having armportions extending from the members 142 and 144 downwardly through theopening 136 in spaced relation with the arm portions a and b of thebimetal elements 26, 28 and 30. The heater elements thus are heated bycurrent flow between the members 142 and 144 and are arranged to heatthe bimetals 26, 28 and 30 in response to the current flow. The member142 has a threaded opening receiving a fastening screw of a wireclamping assembly 148. The wire clamping assembly 148 is arranged tosecure bared ends of an electrical conductor extending from theelectrical load to be monitored and not shown. The member 144 has aportion 150 extending outwardly of a side wall of the switch 10 and ispreferably arranged to be clamped in a wire clamping member on anelectrical switch known as a contactor, in a manner disclosed in [anapplication for U.S. patent, Ser. No. 472,599, filed July 16, 1965,]U.S. Pat. No. 3,304,522, issued Feb. 14, 1967, and assigned by theinventors Joseph J. Gribble and Kenneth J. Marien to the assignee of thepresent invention.

Extending downwardly from the bottom surface of the cover 12b andlocated to be engaged by the arms 26b, 28b and 30b, as shown in FIG. 7,are three spaced stops 48 each integrally formed on the cover 12b andextending into the cavities wherein the bimetals 26, 28 and 30 arepositioned. The stops 48 limit movement of the arms 26b, 28b and 30b asdescribed in connection with FIGS. 1 and 2. Extending downwardly throughthe cover 12b are a pair of spaced openings wherein a leg 152 and theplunger 112 of a reset button are movable. The leg 152, which isintegrally formed with the button portion 157 acts as a guide and issized not to extend into the base 1221, when the button 157 is fullydepressed. The plunger 112 has an end received in a socket 157a in thebutton portion to maintain the button portion 157 and the plunger 112assembled.

A stop portion 158 extending from a sidewall on the plunger 112 isengageable with a bottom surface of the cover 12c to limit upwardmovement of the plunger 112 in the switch 10 by the spring 114. Thespring 114 is positioned in a socket 160 vertically aligned with theopening in the cover 12b through which the plunger 112 extends. Thesocket 160 is formed in the material of the base 12a to receive aportion of the plunger 112 to guide the plunger 112 during its movementsand to present a surface 162 that is engaged by the portion 158 to limitthe downward movement of the plunger 112. The projection 116 is formedas a pair of inclined surfaces 164 and 166 intersecting at an apex 168.The inclined surfaces 164 and 168 are arranged so the bearing surface118 engages a portion of the plunger 112 above the inclined surface 164when the stop portion 158 engages the stop surface 162 and a portion ofthe plunger 112 below the inclined surface 166 when the stop portion 158engages the bottom surface of the cover 12b. As previously described,the apex 168 on the projection is arranged to engage the bearing surface118 for the purpose of moving the flexible mounting strip 104 to aposition whereby the member 76 automatically moves with a toggle actionto the reset position. The plunger 112 additionally is provided with anotch 170 aligned with a slot 172 in the barrier 174 between thecompartments 132a and 132b. A recess 176 in the barrier 174 having abottom wall forming an extension of the slots 172 receives a slide 178.The slide 178 has a portion 178a extending into the slot 172 and ismovable between two extreme positions in the recess 176. When the slide178 is in one position its portion 178a is out of the path of movementof the plunger 112. When the slide 178 is in its second position, asshown in FIG. 7, the portion 178a will be received in the notch 170whereby a bottom edge 170a of the notch 170 engages the portion 178a andmaintains the plunger 112 in a position wherein the apex 168 constantlyengages the bearing surface 118. When the plunger 112 is thus maintainedin position by the slide 178, the flexible mounting strip 104 willposition the contact 70 to cause the toggle action of the member 76 tooccur automatically. Thus when the switch operates in response to anoverload condition wherein the lever 16 causes movement of the member 76to the tripped position wherein the contact 74 engages the contact 70, asubsequent cooling of the bimetals 26. 28 and 30 will remove the forceexerted by the lever 16 on the member 76 and the member 76 willautomatically move with a toggle action to the reset position whereinthe contact 74 engages the contact 72. In normal practice the contact 72is connected in circuit with an operating magnet coil of anelectromagnetically operated switch having contacts controlling circuitsthrough the heating elements H 34, 36 and 38. The contact 70 isconnected in circuit with an alarm or other indicating device. Thus whenthe contact 74 engages the Contact 72, completing the circuit to theoperating coil for operating the electromagnetic switch to complete thecircuits through the heating elements 34, 36 and 38 as well as the loadcircuits monitored by the switch 10, it th overload condition previouslysensed by the switch 10h has ceased to exist, the switch 10 will remainin a reset condition. However, should the overload condition continue,the excess current through the heaters 34, 36 and 38 will cause movementof the bimetal elements 26, 28 and 30 and levers 14 and 16 and actuatethe snap switch 46 to a position wherein the contact 74 moves out ofengagement with the contact 72 and into engagement with the contact 70.As the contact 72 is in circuit with the operating coil of theelectromagnetic switch controlling the load circuit, the load circuitwill be interrupted and the engagement of contact 74 with contact 70will energize an alarm circuit indicating the occurrence of an overloadcondition in the load monitored by the switch 10. Thus when the slide178 is positioned to have the portion 178a within the notch 170, theswitch 10 will be adjusted to operate automatically.

As shown in the drawings, the cover 12b and the base 12a are providedwith a maximum number of openings 180 exposing to a maximum extent theinternal parts of the switch 10 including the bimetal elements 26, 28,30 and 66, as well as the heating elements 34, 36 and 38. The openings180 exposing the bimetal 32 permit the switch 10 to more faithfullyfollow changes in ambient temperatures. The openings exposing theheating elements 34, 36 and 38 as well as the bimetal elements 26, 28,30 and 66, as well as the other elements within the interior of theswitch 10. prevent the transfer of heat to the bimetnl element 32 anddecrease the interval required to reset the switch 10 after the switch10 has responded to an overload condition.

While certain preferred embodiments of the invention have beenspecifically disclosed, it is understood that the invention is notlimited thereto, as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation within the terms of the following claims.

What is claimed is:

l. A thermally operated protective device for use in a plurality ofcircuits wherein N equals the number of circuits, comprising: a fixedstop, a pair of levers movable relative to the stop, a snap switchhaving an operator engaging a first of said pair of levers for actuatingcontacts of the switch when a predetermined force is applied to theoperator by the first lever, N number of identical, heat-response,resilient U-shaped bimetal elements, each of said elements having a pairof ends that move in opposite directions when the element is heated andhaving a first of said pair of ends attached to a second of said pair oflevers and second of said pair of ends positioned to alternately engagethe stop and the first lever and provide a force for moving the leversin opposite directions and the first lever in a direction for actuatingthe snap switch when the bimetal element is heated, N number of heatingunits each connected to be heated by current flow in one of the circuitsand positioned to heat one of the bimetal elements, and means includinga resilient element that is identical to the bimetal elements forresiliently opposing and absorbing movement of the second lever by thebimetal elements in response to the heating of the bimetal elements bythe heating units, said means, second lever and stop being arranged forcausing the second end of any unheated bimetal element to engage thestop when any other bimetal element is heated and for preventingmovement of the first lever by any heated bimetal element until theforce absorbed by the resilient means equals the predetermined forcerequired to move the operator for compensating the operation of thedevice for variations in ambient temperature.

[2. The combination as recited in claim 1 wherein the resilient elementis identical to the bimetal elements and provides a means forcompensating the operation of the device for variations in ambienttemprature] 3. The combination as recited in claim 1 including a heatresponsive means having an operating connection with at least one of thelevers and located to be heated by the heating means at a rate differentthan the bimetal elements for varying the time required to actuate theswitch with variations in the rate of heating of the bimetal elements.

[4. The combination as recited in claim 1 wherein the resilient elementis identical to the bimetal elements and provides a means forcompensating the operation of the device for variations in ambienttemperature and includmg a heat responsive means having an operatingconnection with at least one of the levers and located to be heated bythe heating means at a rate different than the bimetal elements forvarying the time required to actuate the switch with variations in therate of heating of the bimetal elements] 5. The combination as recitedin claim 1 wherein the pair of levers are each pivoted on a portion of ahousing for the device.

6. The combination as recited in claim 5 wherein the pair of levers areparallel and the bimetal elements and resilient element are positionedbetween the pair of levers.

7. The combination as recited in claim 1 wherein the resilient [means]element has a pair of ends with one of the ends being attached to thesecond lever and the other of said ends being attached to a housing forthe device and at least one of the pair of attached ends is attachedthrough a lost motion connection whereby the second lever moves apredetermined distance before the resilient [means] element initiallyopposes further movement of the second lever.

8. The combination as recited in claim 1 wherein the snap switch has amember movable between two operative positions and includes meansresponsive to movement of the operator for moving the member to a firstof said two positions and the deivce includes a member guided by ahousing for the device that has a portion engageable with the snapswitch means for moving the member to a second of said two positions.

9. The combination as recited in claim [4] 3 wherein the heat responsivemeans includes a bimetal element having characteristics difierent thanthe resilient element and having a portion engageable with the secondlever.

10. The combination as recited in claim 1 including means for causingthe first lever to move and actuate the snap switch when any number lessthan all of the bimetal elements are heated to a temperature that islower than the temperature required to actuate the snap switch when allof the bimetal elements are heated.

11. A thermally operated protective device comprising: a fixed stop, aswitch having a movable operator for actuating contacts of the switchwhen a predetermined force is applied to the operator, a first levermovable relative to the stop and having a portion engaging the operator,a second lever movable relative to the stop independently of the firstlever, a plurality of identical bimetal elements each having a first endattached to the second lever and a second end engageable with the stopwhen the second end moves in a first direction and engageable with thefirst lever and supplying a force for moving the first lever and theoperator when the second end moves in a second direction, meansindividual to each bimetal element for heating said elements in responseto current flow in individual circuits and causing movement of the endsof the bimetal elements, and resilient means including a resilientelement that is identical to the bimetal elements, said resilientelement having an end engaging the second lever and resiliently opposingand absorbing movement of the second lever and thereby preventingmovement of the first lever by the bimetal elements when the bimetalelements are heated by the heating means until the force absorbed by theresilient means equals the predetermined force required to move theoperator and actuate the switch contacts.

12. In a thermally operated protective device for use in a plurality ofcircuits wherein N equals the number of circuits, the combinationcomprising: a snap acting switch having a movable operator for actuatingcontacts of the switch when a predetermined force is applied on theoperator, a fixed stop, a pair of levers each movable independentlyrelative to the stop, N number of identical, heatresponsive, resilientU-shaped, bimetal elements, each of said bimetal elements having a pairof ends movable in opposite directions when the bimetal is heated with afirst of said pair of ends being attached to a first of said pair oflevers and a second of said pair of ends being positioned to engage thestop when the second end moves in a first direction and to engage thesecond of said pair of levers when the bimetal is heated and the secondend moves in a second direction, N number of heating elements eachconnected to be heated by current flow in one of the circuits andpositioned to heat one of the bimetal elements, a resilient means havingresilient characteristics identical to the resilient characteristics ofthe bimetal elements, said resilient means having an end engaging thefirst of said levers for resiliently opposing and absorbing movement ofthe first lever and thereby preventing movement of the second lever bythe bimetal elements when the bimetal elements are heated by the heatingelements until the force absorbed by the resilient means equals the predetermined force required to move the operator.

13. An ambient compensated overload relay for use in a plurality ofseparate circuits wherein N equals the number of circuits, said relaycomprising N plus one identical, heat-responsive resilient U-shapedbimetal elements and N number of identical heating units each connectedto be heated by current flow in a respective one of the circuits andpositioned to heat a respective one of the bimetal elements.

14. The overload relay as recited in claim 13 including an additionalheat responsive bimetal element located to be heated by all of theheating units at a rate difierent than the other bimetal elements.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 2,682,005 6/1954 Hemphill et al 317-l3X 2,838,71810/1958 Edmunds 31746 2,928,997 3/1960 Edmunds 31746X 3,031,601 4/1962Rudolph 3 l746 FOREIGN PATENTS 498,325 1/1939 Great Britain.

JAMES D. TRAMMELL, Primary Examiner

